Mitch The objective of this research is to develop a fundamental understanding of the nature of the reduction and nucleophilic substitution reactions occurring between halogenated and nitrated hydrocarbons and sulfides in the presence of black carbons. Using model hydrophobic persistent organic pollutants (POPs) and black carbons, the importance of different sulfide species, black carbon functional groups, and contaminant substituents will be evaluated for contaminant destruction by reduction and nucleophilic substitution pathways. This research will lay the groundwork for the development of an in-situ, abiotic destruction technique for a wide range of POPs in sediment systems that should be less expensive and less environmentally disruptive than current techniques.
Specific hypotheses to be tested include:
1) The presence of black carbon will enhance the degradation of halogenated and nitrated organics in the presence of sulfides compared with reactions conducted in the absence of black carbons. Sorption of contaminants to black carbons will not hinder their destruction.
2) Destruction rates in the presence of hydrogen sulfide will be similar to those in the presence of polysulfides, because the rate-limiting step will be the reaction of the activated quinoid groups in black carbons with the organic contaminant, not the activation of quinoids by sulfides.
3) Contaminant destruction rates will increase with the extent of halogenation or nitration, as the electron-withdrawing nature of these substituents decreases the energy of the lowest unoccupied molecular orbital (ELUMO). Reductions will dominate for nitrated and polyhalogenated compounds, but nucleophilic substitutions will become important for compounds with fewer halogens.
The tasks to test the above three main hypotheses are:
Hypothesis 1 - Correlation of reactivity with black carbon properties Hypothesis 2 - Examination of the relative importance of bisulfide and polysulfides Hypothesis 3 - Correlation of reactivity with contaminant substituent properties
The work will focus on fundamental laboratory studies conducted under environmentally-relevant conditions. Findings of this research will lay the groundwork for future field studies.
For undergraduates, a design class will be developed to be complementary to the PI?s more theoretical Water Quality Control class. It will tackle two projects pertaining to the developed world: a hydraulics project obtained from a local consulting company, and a pilot process project incorporating a laboratory component. The class will also incorporate the design of a water treatment system for a village in the developing world. An Engineers without Borders (EWB) chapter at Yale has already been initiated, with the PI serving as the faculty advisor. The small size of EWB projects enables students to work on an entire water system, including issues such as material availability, and the social and political context that often controls infrastructure projects. The design class will incorporate an actual EWB design project, culminating in an optional summer installation trip.
